I received an email from someone who was perplexed because her N mother as a child was, from all reports, a sweet, compliant and cooperative child to her alcoholic and physically abusive father. The confusion of the emailer prompts me to clarify my point.
It is very possible that the adult narcissist you're dealing with was not considered a problem child by his or her parents, teachers or other authority figures. That is why I emphasized that the problems this narcissist-as-a-child created were most likely felt primarily by their peers, school mates and siblings.
My mother was never in trouble with authority figures. She was not particularly troublesome to her mother. At least, not overtly. (I know she played mind games on her mother, but that was covert behavior which gives her plausible deniability.) The same can be said for my sister. But both my mother and sister as children were demonstrably very different with those who were younger than they were or someone they felt had less power than they had. This meant it was their siblings and peers who felt the effects of the narcissistic behavior patterns of the now grown malignant narcissist.
My male cousin was an example of a young delinquent who presented large problems to authority figures including parents and not just his sibling or peers. I brought him up because even though he was a very difficult child and dangerous teen (clearly sociopathic in addition to extreme narcissism), even he has turned everything around and makes out his family to be what he was. Despite the overwhelming proof that he was the problem, he completely projects all his character and behavior problems onto his family so he can present himself as a victim. My point in mentioning his behavior as a child was to show that no matter the extreme level of perversity they displayed in their youth, they will lie, lie, lie and convince many people they were total victims. Obviously, it is easier for those who were outwardly compliant to parents and other authority figures to try to credibly lay claim to victimhood and/or being "perfect" kids. I just want ya'll to revisit what you've been told and compare it to what you know from your own experience and direct knowledge to know is true. You've likely been given a very white-washed picture of their youth. There are very likely signs that they were well on the path of malignant narcissism from a very young age.